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On July 12, 2017, at 1238 Eastern Daylight … On July 12, 2017, at 1238 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) determined that a preliminary analysis shows adequate Essential Raw Cooling Water (ERCW) flow may not be available during dual unit limiting design basis conditions of one unit in Hot Shutdown on Residual Heat Removal (RHR) cooling when the other unit experiences a Loss of Coolant Accident (LOCA). Based on preliminary analysis, during a Unit 1 LOCA, Unit 1 receives adequate flow when following existing procedural guidance. However, Unit 2 may not receive adequate flow to meet cool-down requirements with design basis maximum temperatures. During a Unit 2 LOCA, however, current procedural guidance is not adequate to ensure the proper system alignment to establish correct ERCW Component Cooling Water (CCS) Heat Exchanger A and B flow rates for either unit's cool down requirements.</br></br>At the time of the event, Unit 2 had been shutdown for an extended period of time such that the flow delivered by ERCW was adequate to serve both Unit 1 in a LOCA and Unit 2 in Mode 4 or 5. Immediate corrective actions included procedure changes to ensure adequate ERCW flow for all possible plant situations in both units. The causes of this issue are a failure to address cross train elements of the ERCW system in the design analysis and a failure to address procedural impacts when the plant transitioned to dual unit operation. The procedure errors were corrected.on. The procedure errors were corrected. +
On July 12, 2017, at 1238 Eastern Daylight … On July 12, 2017, at 1238 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) determined that a preliminary analysis shows adequate Essential Raw Cooling Water (ERCW) flow may not be available during dual unit limiting design basis conditions of one unit in Hot Shutdown on Residual Heat Removal (RHR) cooling when the other unit experiences a Loss of Coolant Accident (LOCA). Based on preliminary analysis, during a Unit 1 LOCA, Unit 1 receives adequate flow when following existing procedural guidance. However, Unit 2 may not receive adequate flow to meet cool-down requirements with design basis maximum temperatures. During a Unit 2 LOCA, however, current procedural guidance is not adequate to ensure the proper system alignment to establish correct ERCW Component Cooling Water (CCS) Heat Exchanger A and B flow rates for either unit's cool down requirements.</br></br>At the time of the event, Unit 2 had been shutdown for an extended period of time such that the flow delivered by ERCW was adequate to serve both Unit 1 in a LOCA and Unit 2 in Mode 4 or 5. Immediate corrective actions included procedure changes to ensure adequate ERCW flow for all possible plant situations in both units. The causes of this issue are a failure to address cross train elements of the ERCW system in the design analysis and a failure to address procedural impacts when the plant transitioned to dual unit operation. The procedure errors were corrected.on. The procedure errors were corrected. +
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04:52:21, 3 March 2018 +
Washington + and Tennessee +
Unanalyzed Condition Related to Dual Unit Operation of the Essential Raw Cooling Water System During a Design Basis Accident +
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